Friction stir welding of containers from the interior

Abstract

An apparatus and method for friction stir welding a seam in a hollow container from the inside. The apparatus includes a weld head convertible between a retracted state to an expanded state. The retracted weld head fits through an opening in the container and then expands to enable formation of the weld. The weld head includes a frame and a least one friction stir welding spindle convertible between a retracted position adjacent the frame and an expanded position away from frame. The container may be a pressure vessel tank, with a circular weld being formed between a tubular mid-section and a hemispherical end cap. Desirably, multiple friction stir welding spindles that expand into a common plane are provided, and relative rotation between the weld head and container forms the circular seam. Force balance arms intermediate adjacent friction stir welding spindles expandable to contact the interior of the container may also be provided to help maintain the position of the weld head. Means for rotating the spindles such as a motor may be provided in the frame. An external anvil hoop may be provided surrounding the seam being welded for further backing support for the internal friction stir welding spindles. Cameras adjacent each weld member monitor the weld process, and may provide visual positioning aids.

What is claimed is:  
     
       1. An apparatus for friction stir welding a seam in a container from the inside, the container being of a type having an opening to the inside, comprising: 
       a convertible weld head having at least one friction stir welding (FSW) spindle mounted thereon adapted to pass through the opening in the container with the FSW spindle in a retracted state and weld the seam from the inside of the container with the FSW spindle in an expanded state, the weld head being too large to fit through the opening of the container with the FSW spindle in its expanded state.  
     
     
       2. The apparatus of  claim 1 , wherein the weld head includes a plurality of FSW spindles. 
     
     
       3. The apparatus of  claim 1 , wherein the weld head includes a central frame and a force balance arm convertible between a retracted state and an expanded state, and wherein in its expanded state the FSW spindle extends outward from the frame in a first direction, and the force balance arm in its expanded state extends outward from the frame in a second direction different than the first direction. 
     
     
       4. The apparatus of  claim 3 , wherein the weld head includes a second FSW spindle and a second force balance arm, and wherein in its expanded state the second FSW spindle extends outward from the frame in a direction opposite the first direction, and the second force balance arm extends outward from the frame in a direction opposite the second direction. 
     
     
       5. The apparatus of  claim 4 , wherein the FSW spindles and the force balance arms extend outward from the frame in substantially the same plane, and wherein the oppositely-directed spindles extend along a line that is 90° offset from a line along which the oppositely-directed force balance arms extend. 
     
     
       6. The apparatus of  claim 1 , wherein the weld head includes a central frame generally aligned along an axis, and at least a pair of FSW spindles that extend outward in opposite directions from the frame in their expanded states. 
     
     
       7. The apparatus of  claim 6 , wherein the FSW spindles pivot with respect to the central frame from their retracted states generally adjacent to the central frame and aligned along the axis, to their expanded states pivoted about 90° away from the central frame with respect to the axis. 
     
     
       8. The apparatus of  claim 6 , wherein the central frame houses a least one motor for rotating the FSW spindles. 
     
     
       9. The apparatus of  claim 1 , further including: 
       a pair of headstocks linearly movable along a common axis, each of the headstocks having thereon one of the weld heads so that the weld heads extend toward each other along the common axis, wherein the apparatus is adapted to simultaneously weld two seams in the container using the two weld heads positioned inside the container.  
     
     
       10. The apparatus of  claim 9 , wherein the container is at least partly tubular and the seams are circular about the ends of the tubular container, the apparatus further including a stand for supporting and rotating the tubular container, wherein the weld heads remain stationary in their expanded states while the tubular container rotates therearound. 
     
     
       11. The apparatus of  claim 1 , further including an anvil adapted to mount to the exterior of the container along the seam and provide backing support for the FSW spindle. 
     
     
       12. The apparatus of  claim 11 , wherein the seam is circular and the anvil is a circular hoop. 
     
     
       13. The apparatus of  claim 1 , further including at least one sensor positioned on the weld head for observing the interior of the container. 
     
     
       14. An apparatus for friction stir welding, comprising: 
       a weld head including a frame and a motor; and  
       a friction stir welding (FSW) spindle having one end pivotally mounted on the frame and coupled to be rotated by the motor, the spindle being adapted to pivot about the one end from a retracted position generally adjacent to the frame to an extended position away from the frame.  
     
     
       15. The apparatus of  claim 14 , wherein the frame is generally aligned along an axis, and wherein the retracted position of the spindle is generally adjacent to the frame and aligned along the axis, and the extended position of the spindle is pivoted away from the frame by about 90° with respect to the axis. 
     
     
       16. The apparatus of  claim 15 , further including a second FSW spindle having one end pivotally mounted on the frame, the second spindle having a retracted position generally adjacent to the frame and aligned along the axis, and an extended position pivoted away from the frame by about 90° with respect to the axis. 
     
     
       17. The apparatus of  claim 16 , wherein the first and second spindles are mounted to pivot on opposite sides of the frame, and wherein the spindles extend in opposite directions in their extended positions. 
     
     
       18. The apparatus of  claim 16 , further including a second motor in the frame coupled to rotate the second spindle. 
     
     
       19. The apparatus of  claim 14 , wherein the frame includes a recess for receiving the spindle in its retracted position and sized so that the spindle does not substantially protrude beyond the recess in its retracted position. 
     
     
       20. The apparatus of  claim 14 , further including a piston/cylinder mechanism mounted to the frame for pivoting the spindle between its retracted and extended positions. 
     
     
       21. The apparatus of  claim 14 , further including at least one sensor positioned on the weld head for observing the interior of the container. 
     
     
       22. The apparatus of  claim 21 , wherein the sensor is a camera having its lens aligned with the FSW spindle to observe the friction stir welding operation. 
     
     
       23. A method for friction stir welding a seam between two sections of a container, the container having an interior space and an opening thereto defining an axis and being smaller than a cross-section of the interior space normal to the axis, the method including: 
       providing a convertible weld head having at least one friction stir welding (FSW) spindle mounted thereon adapted to pass through the opening in the container with the FSW spindle in a retracted state, the weld head being too large to fit through the opening in the container with the FSW spindle in an expanded state;  
       passing the weld head with the FSW spindle in its retracted state from the outside of the container to the interior space through the opening;  
       displacing the FSW spindle from its retracted state to its expanded state; and  
       welding the seam from the inside of the container using the FSW spindle in its expanded state.  
     
     
       24. The method of  claim 23 , further including: 
       after welding the seam, displacing the FSW spindle from its expanded state to its retracted state; and  
       removing the weld head from the container through the opening.  
     
     
       25. The method of  claim 23 , wherein one of the sections of the container is a tube and wherein the seam is circular about one end of the tube, the method including causing relative rotation between the tube and the weld head during the step of welding the seam. 
     
     
       26. The method of  claim 25 , wherein the tube is concentric about the axis of the container opening. 
     
     
       27. The method of  claim 25 , wherein step of causing relative rotation comprises rotating the tube about the axis while holding the weld head stationary. 
     
     
       28. The method of  claim 27 , wherein the container has a second seam and a second opening disposed along the axis, the method further including: 
       providing a second convertible weld head having at least one FSW spindle mounted thereon adapted to pass through the second opening in the container with the FSW spindle in a retracted state, the second weld head being too large to fit through the second opening in the container with the FSW spindle in an expanded state;  
       passing the second weld head with the FSW spindle in its retracted state from the outside of the container to the interior space through the second opening;  
       displacing the FSW spindle in the second weld head from its retracted state to its expanded state; and  
       simultaneously welding the two seams from the inside of the container using the two weld heads with the respective FSW spindles in their expanded states by rotating the tube about the axis while holding the weld heads stationary.  
     
     
       29. The method of  claim 23 , wherein the weld head includes a frame on which the FSW spindle is pivotally mounted, and wherein the step of displacing the FSW spindle from its retracted state to its expanded state comprises pivoting the FSW spindle away from the frame. 
     
     
       30. The method of  claim 26 , further including the step of externally supporting the container at the seam during the step of welding the seam. 
     
     
       31. The method of  claim 27 , wherein the seam is circular, and the step of externally supporting the container comprises securing an anvil hoop around the container at the seam. 
     
     
       32. The method of  claim 23 , further including: 
       observing the interior of the container with at least one sensor on the weld head.